Laminate flooring usually consists of a core of a 6-11 mm fibreboard, a 0.2-0.8 mm thick upper decorative surface layer of laminate and a 0.1-0.6 mm thick lower balancing layer of laminate, plastic, paper or like material. The surface layer provides appearance and durability to the floorboards. The core provides stability, and the balancing layer keeps the board plane when the relative humidity (RH) varies during the year. The floorboards are laid floating, i.e. without gluing, on an existing subfloor. Traditional hard floorboards in floating flooring of this type are usually joined by means of glued tongue-and-groove joints (i.e. joints involving a tongue on one floorboard and a tongue groove on an adjoining floorboard) on long side and short side. When laying the floor, the boards are brought together horizontally, whereby a projecting tongue along the joint edge of one board is introduced into a tongue groove along the joint edge of an adjoining board. The same method is used on the long side as well as on the short side.
In addition to such traditional floors, which are joined by means of glued tongue-and-groove joints, floorboards have recently been developed which do not require the use of glue and instead are joined mechanically by means of so-called mechanical locking systems. These systems comprise locking means which lock the boards horizontally and vertically. The mechanical locking systems are usually formed by machining of the core of the board. Alternatively, parts of the locking system can be formed of a separate material, for instance aluminium, which is integrated with the floorboard, i.e. joined with the floorboard even in connection with the manufacture thereof.
The main advantages of floating floors with mechanical locking systems are that they can easily and quickly be laid by various combinations of inward angling, snapping-in and insertion. They can also easily be taken up again and used once more at a different location. A further advantage of the mechanical locking systems is that the edge portions of the floorboards can be made of materials which need not have good gluing properties. The most common core material is a fibreboard with high density and good stability usually called HDF—High Density Fibreboard. Sometimes also MDF—Medium Density Fibreboard—is used as core.
Laminate flooring and also many other floorings with a surface layer of plastic, wood, veneer, cork and the like are made by the surface layer and the balancing layer being applied to a core material. This application may take place by gluing a previously manufactured decorative layer, for instance when the fibreboard is provided with a decorative high pressure laminate which is made in a separate operation where a plurality of impregnated sheets of paper are compressed under high pressure and at a high temperature. The currently most common method when making laminate flooring, however, is direct laminating which is based on a more modern principle where both manufacture of the decorative laminate layer and the fastening to the fibreboard take place in one and the same manufacturing step. Impregnated sheets of paper are applied directly to the board and pressed together under pressure and heat without any gluing.
In addition to these two methods, a number of other methods are used to provide the core with a surface layer. A decorative pattern can be printed on the surface of the core, which is then, for example, coated with a wear layer. The core can also be provided with a surface layer of wood, veneer, decorative paper or plastic sheeting, and these materials can then be coated with a wear layer. The core can also be provided with a soft wear layer, for instance needle felt. Such a floor has good acoustic properties.
As a rule, the above methods result in a floor element in the form of a large board which is then sawn into, for instance, some ten floor panels, which are then machined to floorboards. The above methods can in some cases result in completed floor panels and sawing is then not necessary before the machining to completed floorboards is carried out. Manufacture of individual floor panels usually takes place when the panels have a surface layer of wood or veneer.
In all cases, the above floor panels are individually machined along their edges to floorboards. The machining of the edges is carried out in advanced milling machines where the floor panel is exactly positioned between one or more chains and bands mounted, so that the floor panel can be moved at high speed and with great accuracy past a number of milling motors, which are provided with diamond cutting tools or metal cutting tools, which machine the edge of the floor panel. By using several milling motors operating at different angles, advanced joint geometries can be formed at speeds exceeding 100 m/min and with an accuracy of ±0.02 mm.
Definition of Some Terms
In the following text, the visible surface of the installed floorboard is called “front side”, while the opposite side of the floorboard, facing the subfloor, is called “rear side”. The sheet-shaped starting material that is used is called “core”. When the core is coated with a surface layer closest to the front side and preferably also a balancing layer closest to the rear side, it forms a semimanufacture which is called “floor panel” or “floor element” in the case where the semimanufacture, in a subsequent operation, is divided into a plurality of floor panels mentioned above. When the floor panels are machined along their edges so as to obtain their final shape with the locking system, they are called “floorboards”. By “surface layer” are meant all layers applied to the core closest to the front side and covering preferably the entire front side of the floorboard. By “decorative surface layer” is meant a layer which is mainly intended to give the floor its decorative appearance. “Wear layer” relates to a layer which is mainly adapted to improve the durability of the front side. In laminate flooring, this layer usually consists of a transparent sheet of paper with an admixture of aluminium oxide which is impregnated with melamine resin. By “reinforcing layer” is meant a layer which is mainly intended to improve the capability of the surface layer of resisting impact and pressure and, in some cases, compensating for the irregularities of the core so that these will not be visible at the surface. In high pressure laminates, this reinforcing layer usually consists of brown kraft paper which is impregnated with phenol resin. By “horizontal plane” is meant a plane which extends parallel to the outer part of the surface layer. Immediately juxtaposed upper parts of two neighbouring joint edges of two joined floorboards together define a “vertical plane” perpendicular to the horizontal plane.
The outer parts of the floorboard at the edge of the floorboard between the front side and the rear side are called “joint edge”. As a rule, the joint edge has several “joint surfaces” which can be vertical, horizontal, angled, rounded, bevelled etc. These joint surfaces exist on different materials, for instance laminate, fibreboard, wood, plastic, metal (especially aluminium) or sealing material. By “joint edge portion” are meant the joint edge of the floorboard and part of the floorboard portions closest to the joint edge.
By “joint” or “locking system” are meant coacting connecting means which connect the floorboards vertically and/or horizontally. By “mechanical locking system” is meant that joining can take place without glue. Mechanical locking systems can in many cases also be joined by gluing.
By “wood-based materials” are meant materials which essentially consist of combinations of wood and/or wood fibres. Examples of such materials are homogeneous wood, wood slats, particle board, plywood, HDF, MDF, compact laminate and like materials. Wood-based materials containing wood fibres can be bound by a binder of the type thermosetting plastic or the like, for instance melamine, phenol or urea. These materials are characterised by good formability by cutting and by exhibiting relatively little thermal expansion. Wood-based material does not include materials containing wood or wood fibres in small amounts only. Nor are wood fibre-reinforced thermoplastics regarded as “wood-based”.
By “strip blank” are meant two or more locking strips which are made by forming a common starting material but which are still in one piece. Examples of such strip blanks will be described in more detail below.
By “fixing” is meant in connection with the locking strip according to the invention that the locking strip should at least be sufficiently attached to the floorboard so as not to incidentally fall off during handling of the floorboard at the factory, during transport and/or in installation. The term “fix” thus does not exclude that the locking strip can be detachable. Nor does the term “fix” exclude that the locking strip, after, for instance at the factory or before installation, being arranged in the joint edge of the floorboard, may be somewhat displaced from its intended position, relative to the floorboard, for instance owing to the fact that the joining of floorboard and locking strip has not been completely performed. Moreover, the term “fix” does not exclude that the locking strip, also when fixed to the floorboard, can be displaceable parallel to the joint edge of the floorboard. By “mechanically fixed” is meant that the fixing is essentially due to shape.
By “snapping” is meant connection which during a first stage occurs by a connecting part being bent or compressed, and during a second stage wholly or partly springing back or expanding.
By “angling” is meant connection that occurs by a turning motion, during which an angular change occurs between two parts that are being connected, or disconnected. When angling relates to connection of two floorboards, the angular motion can take place with the upper parts of joint edges at least partly being in contact with each other, during at least part of the motion.
The above techniques can be used to manufacture laminate floorings which are highly natural copies of wooden flooring, stones, tiles and the like and which are very easy to install using mechanical locking systems. Length and width of the floorboards are as a rule 1.2*0.2 m. Recently also laminate floorings in other formats are being marketed. The techniques used to manufacture such floorboards with mechanical locking systems, however, are still relatively expensive since the machining of the joint portions for the purpose of forming the mechanical locking system causes considerable amounts of wasted material, in particular when the width of the floorboards is reduced so that the length of the joint portions per square meter of floor surface increases. It should be possible to manufacture new formats and to increase the market for these types of flooring significantly if the mechanical locking systems could be made in a simpler and less expensive manner and with improved function.
Prior-Art Technique and Problems Thereof
With a view to facilitating the understanding and the description of the present invention as well as the knowledge of the problems behind the invention, both the basic construction and the function of floorboards according to WO 9426999 as well as the manufacturing principles for manufacturing laminate flooring and mechanical locking systems in general will now be described with reference to FIGS. 1-8 in the accompanying drawings. In applicable parts, the subsequent description of prior-art technique also applies to the embodiments of the present invention that will be described below.
FIGS. 3a and 3b show a floorboard 1 according to WO 9426999 from above and from below respectively. The board 1 is rectangular and has an upper side 2, a lower side 3, two opposite long sides with joint edge portions 4a and 4b, respectively, and two opposite short sides with joint edge portions 5a and 5b, respectively.
Both the joint edge portions 4a, 4b of the long sides and the joint edge portions 5a, 5b of the short sides can be joined mechanically without glue in a direction D2 in FIG. 1c, so as to meet in a vertical plane VP (marked in FIG. 2c) and in such manner that, when installed, they have their upper sides in a common horizontal plane HP (marked in FIG. 2c).
In the shown embodiment which is an example of floorboards according to WO 9426999 (FIGS. 1-3 in the accompanying drawings), the board 1 has a factory-mounted flat strip 6, which extends along the entire long side 4a and which is made of a bendable, resilient aluminium sheet. The strip 6 extends outwards past the vertical plane VP at the joint edge portion 4a. The strip 6 can be mechanically attached according to the shown embodiment or by gluing or in some other way. As stated in said publications, it is possible to use as material of a strip, which is attached to the floorboard at the factory, also other strip materials, such as sheet of some other metal, aluminium or plastic sections. As is also stated in WO 9426999, the strip 6 can instead be formed integrally with the board 1, for instance by suitable machining of the core of the board 1.
The present invention is mainly usable for improving floorboards where the strip 6 or at least part thereof is formed in one piece with the core, and the invention solves special problems that exist in such floorboards and the manufacture thereof. The core of the floorboard need not be, but is preferably, made of a uniform material. The strip 6 is always integrated with the board 1, i.e. it should be formed on the board or be factory mounted.
A similar, although shorter strip 6′ is arranged along one short side 5a of the board 1. The part of the strip 6 projecting past the vertical plane VP is formed with a locking element 8 which extends along the entire strip 6. The locking element 8 has in the lower part an operative locking surface 10 facing the vertical plane VP and having a height of e.g. 0.5 mm. During laying, this locking surface 10 coacts with a locking groove 14 which is formed in the underside 3 of the joint edge portion 4b on the opposite long side of an adjoining board 1′. The strip 6′ along one short side is provided with a corresponding locking element 8′, and the joint edge portion 5b of the opposite short side has a corresponding locking groove 14′. The edge of the locking grooves 14, 14′ facing away from the vertical plane VP forms an operative locking surface 10′ for coaction with the operative locking surface 10 of the locking element.
For mechanical joining of long sides as well as short sides also in the vertical direction (direction D1 in FIG. 1c), the board 1 is also along one long side (joint edge portion 4a) and one short side (joint edge portion 5a) formed with a laterally open recess or groove 16. This is defined upwards by an upper lip at the joint edge portion 4a, 5a and downwards by the respective strips 6, 6′. At the opposite edge portions 4b and 5b there is an upper milled-out portion 18 which defines a locking tongue 20 coacting with the recess or groove 16 (see FIG. 2a).
FIGS. 1a-1c show how two long sides 4a, 4b of two such boards 1, 1′ on a base U can be joined by downward angling by turning about a centre C close the intersection between the horizontal plane HP and the vertical plane VP while the boards are held essentially in contact with each other.
FIGS. 2a-2c show how the short sides 5a, 5b of the boards 1, 1′ can be joined by snap action. The long sides 4a, 4b can be joined by means of both methods, while the joining of the short sides 5a, 5b—after laying the first row of floorboards—is normally carried out merely by snap action, after joining of the long sides 4a, 4b. 
When a new board 1′ and a previously installed board 1 are to be joined along their long side edge portions 4a, 4b according to FIGS. 1a-1c, the long side edge portion 4b of the new board 1′ is pressed against the long side edge portion 4a of the previously installed board 1 according to FIG. 1a, so that the locking tongue 20 is inserted into the recess or groove 16. The board 1′ is then angled down towards the subfloor U according to FIG. 1b. The locking tongue 20 enters completely the recess or groove 16 while at the same time the locking element 8 of the strip 6 snaps into the locking groove 14. During this downward angling, the upper part 9 of the locking element 8 can be operative and perform guiding of the new board 1′ towards the previously installed board 1.
In the joined position according to FIG. 1c, the boards 1, 1′ are certainly locked in the D1 direction as well as the D2 direction along their long side edge portions 4a, 4b, but the boards 1, 1′ can be displaced relative to each other in the longitudinal direction of the joint along the long sides (i.e. direction D3).
FIGS. 2a-2c show how the short side edge portions 5a and 5b of the boards 1, 1′ can be mechanically joined in the D1 direction as well as the D2 direction by the new board 1′ being displaced essentially horizontally towards the previously installed board 1. In particular this can be done after the long side of the new board 1′ by inward angling according to FIGS. 1a-c has been joined with a previously installed board 1 in a neighbouring row. In the first step in FIG. 2a, bevelled surfaces adjacent to the recess 16 and the locking tongue 20, respectively, coact so that the strip 6′ is forced downwards as a direct consequence of the joining of the short side edge portions 5a, 5b. During the final joining, the strip 6′ snaps upwards when the locking element 8′ enters the locking groove 14′, so that the operative locking surfaces 10, 10′ of the locking element 8′ and the locking groove 14′, respectively, come into engagement with each other.
By repeating the operations illustrated in FIGS. 1a-1c and 2a-c, the entire installation can be made without gluing and along all joint edges. Thus, prior-art floorboards of the above-mentioned type can be joined mechanically by, as a rule, first being angled down on the long side and by the short sides, once the long side is locked, snapping together by horizontal displacement of the new board 1′ along the long side of the previously installed board 1 (direction D3). The boards 1, 1′ can, without the joint being damaged, be taken up again in reverse order of installation and then be laid once more. Parts of these laying principles are applicable also in connection with the present invention.
The locking system enables displacement along the joint edge in the locked position after an optional side has been joined. Therefore laying can take place in many different ways which are all variants of the three basic methods                Angling of long side and snapping-in of short side.        Snapping-in of long side—snapping-in of short side.        Angling of short side, displacement of the new board along the short side edge of the previous board and finally downward angling of two boards. These laying methods can also be combined with insertion along the joint edge. Snapping-in occurs mainly by horizontal displacement of the boards towards each other. The locking system may, however, be formed so that snapping-in may occur by a motion which is vertical to or at an angle to the surface of the floorboard.        
The most common and safest laying method is that the long side is first angled downwards and locked against another floorboard. Subsequently, a displacement in the locked position takes place towards the short side of a third floorboard so that the snapping-in of the short side can take place. Laying can also be made by one side, long side or short side, being snapped together with another board. Then a displacement in the locked position takes place until the other side snaps together with a third board. These two methods require snapping-in of at least one side. However, laying can also take place without snap action. The third alternative is that the short side of a first board is angled inwards first towards the short side of a second board, which is already joined on its long side with a third board. After this joining-together, usually the first and the second board are slightly angled upwards. The first board is displaced in the upwardly angled position along its short side until the upper joint edges of the first and the third board are in contact with each other, after which the two boards are jointly angled downwards.
The above-described floorboard and its locking system have become very successful on the market. A number of variants of this locking system are available on the market, above all in connection with laminate floors but also thin wooden floors with a surface of veneer and parquet floors.
Taking-up can be carried out in various ways. All methods require, however, that the long sides can be angled upwards. Then the short sides can be angled upwards or be pulled out along the joint edge. One exception involves small floorboards with a size corresponding to a parquet block which is laid, for instance, in herringbone pattern. These small floorboards can be detached by being pulled out along the long side so that the short sides snap out. The possibility of angling mainly long sides is very important for a well-functioning locking system. Taking-up is usually carried out starting in the first or last row of the installed floor.
FIGS. 5a-5e show manufacture of a laminate floor. FIG. 5a shows manufacture of high pressure laminate. A wear layer 34 of a transparent material with great wearing strength is impregnated with melamine with aluminium oxide added. A decorative layer 35 of paper impregnated with melamine is placed under this layer 34. One or more reinforcing layers 36a, 36b of core paper impregnated with phenol are placed under the decorative layer 35 and the entire packet is placed in a press where it cures under pressure and heat to an about 0.5-0.8 mm thick surface layer 31 of high pressure laminate. FIG. 5c shows how this surface layer 31 can then be glued together with a balancing layer 32 to a core 30 to constitute a floor element 3.
FIGS. 5d and 5e illustrate direct lamination. A wear layer 34 in the form of an overlay and a decorative layer 35 of decoration paper is placed directly on a core 30, after which all three parts and, as a rule, also a rear balancing layer 32 are placed in a press where they cure under heat and pressure to a floor element 3 with a decorative surface layer 31 having a thickness of about 0.2 mm.
After lamination, the floor element is sawn into floor panels. When the mechanical locking system is made in one piece with the core of the floorboard, the joint edges are formed in the subsequent machining to mechanical locking systems of different kinds which all lock the floorboards in the horizontal D2 and vertical D1 directions.
FIGS. 4a-d show in four steps manufacture of a floorboard. FIG. 4a shows the three basic components surface layer 31, core 30 and balancing layer 32. FIG. 4b shows a floor element 3 where the surface layer and the balancing layer have been applied to the core. FIG. 4c shows how floor panels 2 are made by dividing the floor element. FIG. 4d shows how the floor panel 2 after machining of its edges obtains its final shape and becomes a complete floorboard 1 with a locking system 7, 7′, which in this case is mechanical, on the long sides 4a, 4b. 
FIGS. 6a-8b show some common variants of mechanical locking systems which are formed by machining the core of the floorboard. FIGS. 6a, b illustrate a system which can be angled and snapped with excellent function. FIGS. 7a, b show a snap joint which cannot be opened by upward angling. FIGS. 8a, b show a joint which can be angled and snapped but which has less strength and a poorer function than the locking system according to FIG. 6. As is evident from these Figures, the mechanical locking systems have parts which project past the upper joint edges and this causes expensive waste (w), owing to the removing of material performed by the sawblade SB when dividing the floor element and when surface material is removed and the core is machined in connection with the forming of the parts of the locking system.
These systems and the manufacturing methods suffer from a number of drawbacks which are above all related to cost and function.
The aluminium oxide and also the reinforcing layers which give the laminate floor its high wearing strength and impact resistance cause great wear on the tools the teeth of which consist of diamond. Frequent and expensive regrinding must be made particularly of the tool parts that remove the surface layer.
Machining of the joint edges causes expensive waste when core material and surface material are removed to form the parts of the locking system.
To be able to form a mechanical locking system with projecting parts, the width of the floorboard must usually be increased and the decoration paper must also in many cases be adjusted as to width. This may result in production problems and considerable investments especially when manufacturing parquet flooring.
A mechanical locking system has a more complicated geometry than a traditional locking system which is joined by gluing. The number of milling motors must usually be increased, which requires that new and more advanced milling machines be provided.
To satisfy the requirements as to strength, flexibility in connection with snapping-in and low friction in connection with displacement in the locked position, the core must be of high quality. Such quality requirements, which are necessary for the locking system, are not always necessary for the other properties of the floor, such as stability and impact strength. Owing to the locking system, the core of the entire floorboard must thus be of unnecessarily high quality, which increases the manufacturing cost.
To counteract these problems, different methods have been used. The most important method is to limit the extent of the projecting parts past the upper joint edge. This usually causes poorer strength and difficulties in laying or detaching the floorboards.
Another method is to manufacture parts of the locking system of another material, such as aluminium sheet or aluminium sections. These methods may result in great strength and good function but are as a rule significantly more expensive. In some cases, they may result in a somewhat lower cost than a machined embodiment, but this implies that floorboards are expensive to manufacture and that the waste is very costly, as may be the case when the floorboards are made of, for example, high quality high pressure laminate. In less expensive floorboards of low pressure laminate, the cost of these locking systems of metal is higher than in the case where the locking system is machined from the core of the board. The investment in special equipment, which is necessary to form and attach the aluminium strip to the joint edge of the floorboard, may be considerable.
It is also known that separate materials can be glued as an edge portion and formed by machining in connection with further machining of the joint edges. Gluing is difficult and machining cannot be simplified.
Floorboards can also be joined by means of separate loose clamps of metal which in connection with laying are joined with the floorboard. This results in laborious laying and the manufacturing costs is high. Clamps are usually placed under the floorboard and fixed to the rear side of the floorboard. They are not convenient for use in thin flooring. Examples of such clamps are described in DE 42 15 273 and U.S. Pat. No. 4,819,932. Fixing devices of metal are disclosed in U.S. Pat. No. 4,169,688, U.S. Pat. No. 5,295,341, DE 33 43 601 and JP 614,553. EP 1 146 182 discloses sections of thermoplastic which can be snapped into the joint portion and which lock the floorboards with a snap function. All these alternatives have a poor function and are more expensive in manufacture and use than prior-art machined locking systems. WO 96/27721 discloses separate joint parts which are fixed to the floorboard by gluing. This is an expensive and complicated method.
WO 00/20705 discloses joining of floorboards by means of a non-integrated section of extruded thermoplastic. The section has a symmetrical cross-section and all shown sections allow only joining of floorboards by means of different snap joints. Such loose sections make laying of the floorboards more complicated and time-consuming.